linux-kernel - Re: [PATCH] Input: elan_i2c - check if device is there before really probing

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Message-ID: <bfb8af3c-c338-5942-ab61-31cf298aa410@roeck-us.net>
Date:   Wed, 3 May 2017 23:42:54 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-input@...r.kernel.org
Cc:     KT Liao <ktalex.liao@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: elan_i2c - check if device is there before really
 probing

On 05/03/2017 11:29 PM, Dmitry Torokhov wrote:
> Before trying to properly initialize the touchpad and generate bunch of
> errors, let's first see it there is anything at the given address. If we
> get error, fail silently with -ENXIO.
>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> ---
>  drivers/input/mouse/elan_i2c_core.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/input/mouse/elan_i2c_core.c b/drivers/input/mouse/elan_i2c_core.c
> index 5d3b53dd2fa2..0479730e7c5c 100644
> --- a/drivers/input/mouse/elan_i2c_core.c
> +++ b/drivers/input/mouse/elan_i2c_core.c
> @@ -1040,6 +1040,7 @@ static int elan_probe(struct i2c_client *client,
>  	const struct elan_transport_ops *transport_ops;
>  	struct device *dev = &client->dev;
>  	struct elan_tp_data *data;
> +	union i2c_smbus_data dummy;
>  	unsigned long irqflags;
>  	int error;
>
> @@ -1091,6 +1092,14 @@ static int elan_probe(struct i2c_client *client,
>  		return error;
>  	}
>
> +	/* Make sure there is something at this address */
> +	error = i2c_smbus_xfer(client->adapter, client->addr, 0,
> +			       I2C_SMBUS_READ, 0, I2C_SMBUS_BYTE, &dummy);

Can't you just call i2c_smbus_read_byte_data(client, 0); and check if it returns
an error ?

Thanks,
Guenter

> +	if (error) {
> +		dev_dbg(&client->dev, "nothing at this address: %d\n", error);
> +		return -ENXIO;
> +	}
> +
>  	/* Initialize the touchpad. */
>  	error = elan_initialize(data);
>  	if (error)
>